1. Field of the Invention
The present invention relates to a method for the gasification of coal, more specifically to a method for the gasification of coal wherein electric power generated by wind power, waterpower or solar energy can be effectively utilized.
2. Description of the Prior Art
Partial oxidation gasification and hydrogenation gasification are known as conventional methods of coal gasification. An efficiency to produce clean gas from coal is only about 70% in the former and no more than 75% even in the latter, which is the latest method.
The following Table 1 shows an example of heat balance in the partial oxidation gasification.
TABLE 1Heating value perkg of coalHigher heating value (HHV) of feed coal7330Kcal/kgHeating value of gas generated from6050Kcal/kga gasifierAmount of gasification gas consumed−910Kcal/kgin the gas cleaning processesAvailable energy5110Kcal/kgEfficiency70.1%
As described above, in the conventional partial oxidation gasification, about 70% of the HHV of the coal, 7330 Kcal/kg, is available as a clean gas. In the conventional partial oxidation gasification, a part of feed coal is burnt to generate electricity or steam which is used for air separation to produce oxygen, as described in Jan Eurlings, Europower, 55–61,winter 1993, and in U.S. Department of Energy Office of Fossil Energy, “Market-based Advanced Coal Power Systems, Final Report,4.1.4.9, May 1999. ” As a result, an efficiency of producing clean gas in the coal gasification is no more than about 70% and an emission of carbon dioxide is not reduced. This prevents one from utilizing gases produced by the conventional coal gasification. Moreover, coal emits more carbon dioxide per unit heating value than petroleum or natural gas, so that its use is under restriction to prevent the greenhouse effect.
An integrated system of photovoltaics (PV) and an integrated coal gasification combined cycle (IGCC) is described in S. W. Gouse et al., “Integration of Fossil and Renewable Energy Technologies to Mitigate Carbon Dioxide”, Energy Convert. Mgmi Vol 34, No. 9–11, 1023–1030, 1993. In the system, the PV plant is equipped with an electrolyzer to produce hydrogen and oxygen from water. The object of the invention is to mitigate carbon dioxide from IGCC and, therefore, none of the present features to improve a gasification efficiency is described.